Sketchup Help with Union

I wonder if someone here might know why this is happening. I have a file in sketchup 8 pro. It contains several solid parts i'm trying to combine into a single solid mesh through the use of the union tool. The parts are organic in form and so their triangle count is fairly high but not beyond that of sketchup.
Whenever i use the union function on these models the results randomly float between one of the two selected parts just disappearing or them both combining but the union doesn't remove any interior geometry almost like it had run an intersect with model command instead.
the models are meant to be 25mm miniatures but they have been scaled up by a factor of almost a million. I've tried the union opeartion with a lot of varient parts and sometimes it happens sometimes it doesn't its quite frustrating. I've even tried reinstalling sketchup and removing all my plugns but it continues to have the error.
I've attached two links to two sketchup files. the first is a copy of the figure with the solid parts seperate. the second is an example of what I get when i union the parts.
https://docs.google.com/open?id=0B3f58gvQLC00Y2ZiZjRiMzAtYTJ lNC00YjZjLWI1YmYtMGZkZmRlNTZiZmE2

https://docs.google.com/open?id=0B3f58gvQLC00YzgxY2U1M2EtM2R kOC00MWRmLThhMTQtNWNkMTA2MjYyM2Rk

If anyone can shed some light on what's happening I'd be greatful.

I think its because the groups are overlapping in multiple places, and Sketchup doesn't know which group is supposed to be in or out. I've colored the groups separately and added arrows to where I think the problem is.


Nice model, BTW!

ok I guess that makes sense. I've tried scaling the model and shifting things around but it doesn't really change how it unions perhaps if I redesign the parts a bit I can eliminate the overlaps that come through.

I've seen a lot of problems with Sketchups Union lately. But why are you joining them? If you upload to shapeways, as long as the triangles are not overlapping, shapeways will automatically join them for you so you don't get charged twice for overlapping geometry.

I'm joining them mostly because I have come to realize many of my other printing problems are directly caused by geometry errors I can't see. On several occasions they have been caused by overlapping shells. While I realize the geometry won't cost me more money it costs me more time every time I have to troubleshoot problems.
Beyond this shapeways does have two limits that this type of geometry will play havoc with. The triangle and file size limit. This model on its own is only something like 40,000 triangles. However the intent is to make sets of 5 legs as well as a full unit set which includes 5 with torso, arms, head, and weapons. the over lapping geometry doesn't really affect a single part of the model right now but once I have the legs, arms, torso, heads, guns, and swords in a single file it pushes the limit and eliminating the unseen geometry is a good solution.
Additionally there is the issue of shells. While shapeways allows multiple shells per model now they might not be so accepting in the future. The shell issue has always been a touchy one and presently, like wall thickness, it's entirely in the eye of whoever is at the printer at the time the order is placed. Considering that model alone breaks into a minimum of 28 shells and then I want to add more parts in including multiple copies of it... I think I'm rather close to the limit of the printer's benevolence as is.
Ultimately though I guess I just think unionizing the parts is the right way to make the model, for me at least. It makes it more likely to print and less problematic to work with and store. I rarely see source models on 3d model sights that have a massive amount of loose geometry sitting in them so I figured they must be doing something right.